Nu-carboanhydrides and polymers therefrom



Patented July 7, 1953 UNITED STATES PATENT OFFICE N-CARBOANHYDRIDES AND POLYMERS THEREFROM Merlin Martin 'Brubaker, Chadds Ford, Pa., and

Robert Neal MacDonald, New Castle, Del., assignors to E. I. du Pont de N emours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application Decemb r 7,1948,

' Serial No. 64,042

polymerization of a mixture of the N-carboan hydrides of L-leucine and DL-phenylalanine.

However, polyamides from this type of alphaamino acid (1. e., those containing at least one hydrogen on the alpha-carbon) are relatively poor in heat resistance and thus suffer thermal degradation at temperatures lower than those desired for high quality polyamides. Further- 13 Claims. (01. zoo-"ray more, the N-carboanhydrides of this type of alpha-amino acid are in themselves relatively poor in heat resistance and decompose at relatively low temperatures with concomitant polymerization, thus making their preparation and purification to the high level necessary for good polymer formation more diflicult and muchless efficient.

N-carboanhydrides of amino hydrogen-con taining alpha-amino acids whose alpha-carbon is an annular member of a cycloaliphatic ring are disclosed in the copending application of MacDonald, Serial No. 766,458, filed August 5, 1947. N-carboanhydrides can be polymerized and copolymerized, for example, with the N-carboanhydrides of other types of amino acids to form.

linear polyamides. Although polyamides from this type of alpha-amino acid exhibit greatly improved thermal stability, they are not soluble'in as wide a range of organic solvents as is desired.

This invention has as an object the preparation of N-carboanhydrides of improved thermal stability. A further object is the preparation of more readily purified N-carboanhydrides. Another object is the preparation from 'N-carboanhydrides of thermally stable condensation polyamides soluble in a wide range of organic solvents. Other objects will appear hereinafter.

These objects are accomplished by the invention of N-carboanhydrides of alpha-amino-acids which acids have primary alkyl groups on the alpha-carbon, i. e., the carbon bearing the car- This application also discloses that these.

amino nitrogen and have atotal of three to six carbons on the amino nitrogen and alpha-carbon, i. e., by the invention of N-carboanhydrides of saturated aliphatic monoamino monocarboxylic acids containing only five to eight carbons, hydrogen, the one amino nitrogen and the two carboxyl oxygens and the preparation from these N-carboanhydrides, by thermal condensation with carbon dioxide evolution, of condensation polymers characterized by recurring units l I NCOO wherein R' and R are primary alkyl groups and R." is CnH2n+l where n is a cardinal number and the total number of carbons in R, R, and R' is from 3 to 6. Y

The new polyamides of this invention .are outstanding in thermal stability as compared with the alpha-amino acid polyamides previously known inthe art. In addition,- they exhibit good solubility in awide range of organic solvents, thus making them as readily handleable in normal solution casting and wet spinning procedures as any of the alpha-amino acid polyamides previously known. Thus, a polymer from the N-carboanhydride of. alpha-amino-alpha-v methylbutyric acid, one of the novel N-carboanhydrides of this invention, remains on a copper block heated to 225 C. and exposed to the oxidative degradationof the airfor three hours without evidencing' any visible "changes in appearance or properties. vIn contrast, a polyamide from a 1:1 mixture, by Weight, of the N- carboanhydrides of L-leucine and DL-phenylal- V anine under the same conditions discolors noticeably, becomes appreciably dark, and loses a great deal of its strength in only two minutes. Both of these polyamides exhibit approximately the same solubilities in organic solvents. The polyamide from the N-carboanhydride of 1-aminocyclohexanecarboxylic acid (a representative alpha-amino acid whose alpha-carbon is an annular member of a cycloaliphatic ring) while exhibiting the same high thermal insensitivity as the above-noted polyamide from the N-carboanhydride of alpha amino alpha-methylbutyric acid is generally insoluble in organic solvents.

However, as noted above, the polyamide from the N-carboanhydride of alpha-amino-alphamethylbutyric-acidis soluble in a wide range of normally used'organic solvents, such as for example chloroform and m-c'r'esol. boxyl nd am n p av hy r n on theta The novel N-carboanhydrides of this invention are markedly more heat resistant, i. e., more thermally stable than the previously known N-carboanhydrides of alpha-amino acids. They can be heated to higher temperatures before evidencing any appreciable sign of thermal decomposition and subsequent polymerizationa very valuable property since it allows the preparation of these N-carboanhydrides to be carried out at higher reaction temperatures than are possible with most of the N-carboanhydrides previously known. This increased thermal stability also allows these N-carboanhydrides to be purified by repeated recrystallizations at higher solution temperatures with no concomitant loss by thermal condensation, thus making easier and more efficient their purification to the high levels of purity necessary for their molecular weight polyamide formation. Although this property of greater thermal stability makes it somewhat more difficult to polymerize these N-carboanhydrides thermally, the advantages gained in the preparation of the N-carboanhydrides overbalances this difficulty.

The N-carboanhydrides may be prepared from the corresponding amino acids by the method of Leuchs, Ber. 39, 857-861 (1906), which can be represented by the following equations:

where R, R, and R are as previously, A is alkyl or aralkyl and X is halogen.

They may also be prepared from the amino acids Or their alkali or alkaline earth metal salts and phosgene as described in the copending application of MacDonald, Seria1 No. 778,458, filed October 7, 1947, or from the amino acids, their alkali or alkaline earth metal salts, or their hydrohalide salts and phosgene in the presence of a hydrocarbon ether as described in the copending application of W. W. Prichard, Serial No. 52,971, filed October 5, 1948. Thes methods may be represented by the following general equation:

RNH

(or the hydrohalide salt) wherein R, R, and R" are as given previously, HX is a hydrohalide and M is hydrogen or an alkali or alkaline earth metal.

The N-carboanhydrides may also be prepared by the method disclosed in the copending application of W. W. Prichard, Serial No. 778,457, filed October 7, 1947, now Patent No. 2,516,145. The method comprises treating an alpha-amino acid having at least one hydrogen atom on the nitrogen in an anhydrous solvent with an alkali metal alkoxide and with carbon dioxide thereby forming the dialkali metal salt of the alpha-carboxyaminocarboxylic acid and reacting under anhydrous conditions thionyl chloride with said dialkali metal salt of the alpha-carboxyaminocarboxylic acid to form the N-carboanhydride.

These N-carboanhydrides, taken singly or in mixtures with themselves or other N-carboanhydrides, at least of such N-carboanhydride mixture consisting of one or more N-carboanhydride of this invention can be polymerized, in bulk or in solution, with decomposition attended by carbon dioxide evolution, thermally, or initiated by water, alcohols, phenols, or by amino hydrogen-bearing amines as disclosed in the copending application of MacDonald, Serial No. 778,032, filed October 4, 1947. This polymerization is represented by the following equation, utilizing a general formula for the N-carboanhydrides of this invention, where the Rs are as given previously:

Thus the polyamides of this invention are characterized by a plurality of recurring The following examples in which parts are by weight are illustrative of the invention.

EXAMPLE I PREPARATION or THE N-CARBOANHYDRIDE or N-lilErHY'L-ALPHA-AMINoIsoBUrYmo ACID Preparation of N-methyZ-N-carbobenzyloxyalpha-aminoisobutyric acid To a mixture of 20 parts of sodium hydroxide dissolved in 255 parts of water and 58.5 parts of N-methyl-alpha-aminoisobutyric acid are added simultaneously during agitation at ice-bath temperature 85.3 parts of carbobenzyloxy chloride (prepared as described in Organic Syntheses, volume XXIII, page 13) and a solution of 20 parts of sodium hydroxide dissolved in 127.5 parts of water over a period of one hour in such a fashion that the acid chloride is in excess of the alkali until the end of the acylation. After being stirred for an additional two hours in an ice-bath, the reaction mixture is extracted several times with ether and made acid with concentrated aqueous hydrochloric acid at 10 C. The white crystalline precipitate so obtained is removed by filtration, freed of chloride ions by repeated washings with Water and dried in a vacuum desiccator over anhydrous calcum chloride under reduced pressure. There is thus obtained 43 parts (34% of theory) of N methyl N carbobenzyloxy alphaaminoisobutyric acid as colorless crystals melting at -121 C.

AnaZysis.Calculated for C13H17NO42 N, 5.58%; acid number 223.3. Found: N, 5.76%; acid number 223.5.

Preparation of the N-carboanhydride of N- methyl-alpha-aminoisobutyric acid In a reactor open to the atmosphere only through a drying tube, eight parts of the above N methyl N carbobenzyloxy alpha aminoisobutyric acid is mixed with 21.3 parts of thionyl chloride. Vigorous evolution of sulfur dioxide and hydrogen chloride begins at once. The reaction mixture is allowed to stand at room temperature over night and the thionyl chloride is removed. from the resulting clear solution by distillation under reduced pressure. The residue is washed thoroughly with petroleum ether and the solid product (2.85 parts 66% of theory) removed by filtration under anhydrous conditions. This product is then extracted with 70.8 parts of anhydrous diethyl ether and the undissolved portion removed by filtration. Petroleum ether is added slowly with stirring to the clear, ether filtrate until a slight cloudiness is obtained. The solution is then cooled in an ice-saltbath, and the solid precipitate formed is removed by filtration. There is thus obtained 1.15 parts (27% of theory) of pure N-carboanhydrideof N-methylalpha-aminoisobutyric acid as colorless crystals melting at 62.963.l C.

AnaZysis.Calculated for C6H9NO3I C, 50.34%; H, 6.34%; N, 9.79%. Found: C, 50.7 H, 6.39%; N, 9.89%.

The N-carboanhydrides may be prepared not only, as above, by the method of Leuchs et'al. as applied to alpha-amino-alpha,alpha-diprimaryalkylacetic acids, but also, as in Example II below, by the method of W. W. Prichard, Serial No. 52,971, filed October 5, 1948, applied to these acids.

EXAMPLE II PREPARATION or THE N-OARBOANHYDRIDE or H N-DJETHYL-ALPHA-AMINOISOBUTYRIC' Acn) Gaseous phosgene is slowly passed into a wellstirred suspension of parts of N -methyl-alphaaminoisobutyric acid hydrochloride in 300 parts of purified, anhydrous dioxane in a reactor open to the atmosphere only through a drying tube and equipped with a reflux water condenser and entry and exit ports, while maintaining the temperature at 80 C. until 9.8 parts (100% of theory) of phosgene is added. The reaction mixture is cooled to room temperature and the insoluble portion [3.6 parts (24% recovery) of unreacted N-methyl-alpha-aminoisobutyric acid hydrochloride] is removed by filtration under anhydrous conditions. The dioxane is removed from the clear filtrate by distillation and sufiioient petroleum ether is added with stirring to the resulting concentrate to precipitate the N-carboanhydride which is then removed by filtration. There is thus obtained six parts (43% of theory) of the White, crystalline N carboanhydride of N- methyl-alpha-aminoisobutyric acid.

The preparation of homopolyamides and copolyarnides from the N-carboanhydrides of this inevntion is illustrated in Examples III through VI below using the N-carboanhydride of N- methyl-alpha-aminoisobutyric acid.

EXAMPLE III PoLYAMroE FROM THE N-GARBOANHYDRIDE or N-METHYL-ALrHA-AMINoIsoBUTYRic ACID One part of the N-carboanhydride of N- methyl-alpha-aminoisobutyric acid is heated at 6 EXAMPLE Iv GoPoLYA mE FROM A 1: 1 MIXTURE or THE N-CAImo- ANHYDRIDES 0F N-METHYL-ALPHA-AMINOISOBU- TYRIC ACID AND l-AMINOOYOLOHEXANEGARBOXYIJO Aon) GoPoLYAMIDE FROM A 1:1 MIXTUREDF THE N-fCABBO- HxnBIDEs or N -l\IETHYL-ALPHA-AMINOISOBU- TYRIC AoIo AND ALPHA-AMINOISOBUTYRIO A011) A mixture of fiv parts each of the N-carboanhydrides of N-methyl-alpha-aminoisobutyric acid and alpha-'aminoisobutyric acid and 0.022 part (0.3 mole per cent based on the total N- carboanhydrides) of cyclohexylamine in 217 parts of xylene is heated for ten days at C. There is thus obtained a high molecular weight copolyamide of N-methyl-alpha-aminoisobutyric acid and alpha-aminoisobutyric acidas a white, infusible powder, soluble in m-cresol. This polymer withstands heating at elevated temperatures more than twice as long as the copolyamide from a 1:1 mixture of the'N-carboanhydrides, of L-leucine and DL-phenylalanine before discoloration can 'be noted.

EXAMPLE 'VI CoPoLY MIoE FROM A 1: l MIXTURE on THE N-CARBO- ANHYDRIDES or N-METHYL-ALPHA-AMINoIsOBU- TYRIC Aon) AND 2-AMINO-4,6,6-TRIMETHYLHEP- TANOIC Aoro EXAMPLE VII PREPARArIoN or THE N-GARBoANHYDRIoE or ALPHA- AMINODIETHYLACETIC A011) Preparation of 'N-carbobenzylory-alpha-aminodiethylacetic acid To a mixtureof 106 parts of 2.015 N sodium hydroxide solution and 26 parts of alpha-aminodiethylacetic acid are added simultaneously during agitation at ice-bath temperature 56.5 parts of 4.029 N sodium hydroxid solution and 34.1 parts of carbobenzyloxychloride over a period'of 50 minutes in such a fashion that the acid chloride is in excess of the alkali until the end of the acylation. After being stirred for'an additional one hour in an icebath, the reaction mixture is extracted several times with ether and made acid with concentrated aqueous hydro-v chloric acid at C. The white, pasty mass so obtained is removed by filtration and dissolved in ether. The aqueous filtrate is extracted several times with ether and this extract combined with the ether solution. The combined solution is washed three times with cold salt water, twice with cold distilled water and then dried overnight over anhydrous calcium sulfate. The ether is removed by distillation under reduced pressure. There is thus obtained 14.4 parts (27% of theory) of N carbobenzyloxy-alpha-aminodiethylacetic acid as white crystals melting sharply at 965 C.

AnaZysis.Calculated for C14H19NO4Z Acid number 211.5; N, 5.28%. Found: Acid number 212.6; N, 5.33%.

Preparation of the N-carboanhydride of alphaaminodiethylacetic acid In a reactor open to the atmosphere only through a drying tube, 3.8 parts of the above N-carbobenzyloxy-alpha-aminodiethylacetic acid is mixed with 17.7 parts of thionyl chloride. Evolution of sulfur dioxide and hydrogen chloride begins after about fifteen minutes. The reaction mixture i allowed to stand at room temperature overnight, and the thionyl chloride is removed from the resulting clear solution by distillation at ice-bath temperature to 40 C. under pressures of from 16 to 2 millimeters of mercury. The resulting oil is heated for one hour at 100 C. under a pressure of 2 millimeters of mercury. The thick oil so obtained is found by analysis to contain 8.74% N. Th theoretical value for the N -carboanhydride of alpha-aminodiethylacetic acid (C'IH11NO3) is 8.88% N. Upon standing this oil become crystalline. After recrystallization from ether/petroleum ether mixture there are obtained white crystals of the N-carboanhydride of alpha-aminodiethylacetic acid melting at 45-4'7 C. (capillary tube in melting point bath).

EXAMPLE VIII PREPARATION or THE N-GABBOANHYDRIDE or ALPHA- AMINODIE'IHYLACETIC ACID Gaseous phosgene is slowly passed under a positive pressure of 2 millimeters of mercury into a well-stirred suspension of ten parts of alphaaminodiethylacetic acid in 300 parts of purified, anhydrous dioxan in a reactor open to the atmosphere only through a drying tube and equipped with a reflux water condenser and entry and exit ports, while maintaining the temperature at 100 C. until 8.3 parts (110% of theory) of phosgcne is added, at which point the suspended amino acid is all dissolved. The reaction mixture is passed through a stripping still at 70 C. under 30 millimeters of mercury pressure to remov most of the dioxane. The remaining traces of the solvent are removed from the residue by heating in a vacuum oven at 78 C. under 0.5 millimeters of mercury pressure for four hours. The resulting colorless oil is taken up in fifteen parts of anhydrous diethyl ether and petroleum ether is added with stirring until no further precipitation occurs. The resulting slurry is cooled in an ice-bath, and the precipitate is removed by filtration under anhydrous conditions. There is thus obtained 7.3 parts (61% of theory) of the N-carboanhydride of alpha-aminodiethylacetic acid as colorless crystals melting at 43 C. (melting point block).

Analysis.Calculat ed for C'zHnOsN: C, 53.5%; H, 7.0%; N, 8.92%. Found: C, 53.6%; H, 7.1%; N, 8.88%-

8 EXAMPLE IX POLYAMIDE FROM THE N-CABBOANHYDRIDE or ALPHA-AMINODIETHYLACETIC Acn) A mixture of one part of the N-carboanhydride of alpha-aminodiethylacetic acid and 0.001 part (0.16 mole per cent based on the N-carboanhydride) of cyclohexylamine is heated in a narrow reactor open to the atmosphere at one end for five hours at 218 C. There is thus obtained a high molecular weight alpha-aminodiethylacetic acid polyamide as a white, thermally stable solid, soluble in m-cresol.

EXAMPLE X PREPARATION or THE N-Camsosunrnmns or ALPHA- AMINO-ALPHA-METHYLBUTYRIC Acm Preparation of N-carbobenzyloxy-alpha-aminoalpha-methylbutyric acid To a mixture of 28.2 parts of sodium hydroxide dissolved in 1,000 parts of water and 82.6 parts of alpha-amino-alpha-methylbutyric acid are added simultaneously during agitation at icebath temperature 124.5 parts of carbobenzyloxy chloride and a solution of 28.8 parts of sodium hydroxide dissolved in 180 parts of water over a period of 45 minutes in such a fashion that the acid chloride is in excess of the alkali until the end of the acylation. After being stirred for an additional 1.5 hours in an ice-bath, the reaction mixture is extracted several times with ether and made acid with concentrated aqueous hydrochloric acid in the cold. The white oil which separates is taken up in ether and the ethereal solution treated with a saturated aqueous solution of sodium bicarbonate (50% excess). The water layer which separates is treated with decolorizing charcoal, filtered, cooled to 10 C. and acidified with concentrated aqueous hydrochloric acid. The pasty mass which precipitates is removed by filtration, freed of chloride ions by repeated washings with water, and dried in a vacuum desiccator over anhydrous calcium sulfate under reduced pressure. There is thus obtained '70 parts (39.5% of theory) of N-carbobenzyloxy- 62.15%; H, 6.82%; N, 5.58%. Neutral equivalent 251.3. Found: C, 62.31%; H, 6.93%; N, 5.34%. Neutral equivalent 250.3.

Preparation of the N-carboanhydride of alphaamino-alpha-methylbutyric acid In a reactor open to the atmosphere only through a drying tube, a mixture of 25.1 parts of the above N-carbobenzyloxy-alpha-amino-alphamethylbutyric acid, 23.8 parts of thionyl chloride, and 85.0 parts of anhydrous diethyl ether is refluxed for 4.5 hours. The reaction mixture is allowed to stand at room temperature for an additional 12 hours and then poured into 400 parts of petroleum ether. The clear solution so obtained is cooled in an ice-salt bath for one hour and the solid product which precipitates is removed by filtration under anhydrous conditions. There is thus obtained 10.2 parts (71% of theory) of crude N-carboanhydride of alpha-aminoalpha-methylbutyric acid. The crude material is purified by dissolving in warm anhydrous diethyl ether, treating with decolorizing charcoal, and filtering. It is finally recrystallized by adding excess petroleum ether and cooling. The crystalline product so obtained is removed by filtration under anhydrous conditions. There is thus ob- 91 tained 8.13 parts: (57% .of theory); of the-pure N- carboanhydride 'of alpha-amino-alphaemethyle butyric acid as fine, colorless needles melting sharply at 65.5 C. "I

AnaZysis.-Calculated for CGHQNOSI C, 50.34%; H, 6.34%; N,. 9.79%.. ...Found:.=C,.50.70%; H, 6.39%; N, 9.75%. 1

BULK PoLYMERIzA'rIoN on THE N-O aeoA HYnRmE F ALPHA-Atario-ArlrHA-MErrrxtnUrmq A mixtureof five parts of the N-carboa'nhydride of alpha-amino-alpha methylbutyricacid and 0.01 part (0.3-mole per:cent based on 'N carboanhydride). of=tetramethylenediamine is heated'ina narrow vessel-open to the atmosphereat one end for 4.5 hours: at 146?. C.'- The-'high 'molecular weight polyamide of alphaarnino alpha-methyl butyric acid thusobtained is a hard, brittle, thermally stable solid-,soluble in m-cresol and softening at 260 C. I

EXAMPLE XII SOLUTION POLYMERIZATION or THE N-GaRnoANny- DRIDE 0F ALPHA-AlumO-ALrHA-MET MUTYRIo ACID A mixture of five parts of the N-carboanhy.-.

dride of alpha aminoealpharmethylbutyric acid,

0.005 part (0.14 mole per centbased on.N-carbo-. anhydride) of cyclohexylamine and 166 parts ofchlorobenzene is heatedat 125C. for seven days. The high molecular weight; polyamlde of alpha: amino-alpha-methylbutyric acid thus obtained is an infusible powder, solublein chloroform and m,- cresol. When placed ona copper block for three, hours at 225 C. exposed to air, novisible change is noticed, Whereas a copolyamicle froma 1 :1 mix-,

ture of the N-carboanhydride of L-leucine and DL-phenylalanine polymer discolors'within two. minutes at this temperature/and the polyamide from the Nca rboanhydrides of .alpha-aminomyristic and alpha-aminolauric acids discolor within two and live. minutes, respectively- EXAMPLE-XIII GoPoLYAiuiDE From A' 1:31 MIxrUBE or THEN-Clinto- HYDRIDES OF ALPHA' AMiNo-ALPHA METHYLBU- 'rYaro Aorn AND 'I-AMINOCYCLOHEXANEOABBOXYLIG A mixture of five parts each of the N -carboan hydrideg of alpha-amino-alpha methylbutyric acid and 1aminocyclohexanecarboxylic acid,

0.0.05 part (0.08 mole per cent based on the total.

N-carboanhydrides) of cyclohexylamine and 332 parts of chlorobenzene is heated 'at 125". C. for seven days." The high;- molecular' weight copolyamide of alpha-amino-alphamethylbutyric acid and 1-aminocyclohexanecarboxylic acid thus ob-. tained is an infusible solid, soluble in chlorobenzene and 'inboiling m-cre'sol. No discoloration is noted after three hours on a copper block at 225 v C. in the air comparedjtlo marked discoloration under thoseconditions i'ntwominutes for 'a.c'o-' polyamide from a 1 :1 mixture of the N-carb'oanhydrides of L-leucine and DL-phenylalanine, respectively, for the polyamides from'the N-carbo-' anhydrides of alpha-aminomyristic and alphaaminolauric acids. 7 I

, EXAMPLE XIV PREPARATION or THE N Osrmonnrrrnnipn or ALPHA- AMINO-ALPHA,GAMMA-DI'METHYLVALERIo Acrn Preparation. of Ncarbo b'eneyZoxy-aZph -amino dissolved in 272 parts of water and 80. parts of alpha-amino-alpha,gamma-dimethylvaleric acid are added simultaneously with stirring at icebath temperature 93.8 parts of carbobenzyloxy chloride and a solution of 22 parts of sodium hydroxide dissolved in 136 parts of water over a period of 4.5 minutes in such a fashion that the acid chloride is in excess of the alkaliuntil the end of the acylation. After being stirred for an additional 1.5 hours in an ice-bath, the reaction mixture is extracted with ether several times and made acidwith concentrated aqueous hydrochloric acid in the cold. 1 The thick oil thus obtained crystallizes to a white solid upon standing. This crude product is filtered, freed of chloride ions by repeated washings with water and dried. There is thusobtained 96.3 parts (63% of theory) of crude N-carbobenzyloxyalphaeamino-alpha,gamma-dimethylvaleric acid as whitecrystals, melting at 111 C.

To a solution of 10 partsof the above material in 66 parts of warm benzene is added 99 parts of warm petroleum ether. The product crystallizes from the'resulting clear solution upon standing and is removed by filtration. After drying there is thus obtained 8.2 parts of pure N-carbobenzyloxy alpha amino alpha,gamma dimethylvaleric acid as colorless crystals, melting at lib-116 C.

AnaZysis.Calculated for C15H21NO4: C, 64.5%; H, 7.58%; N, 5.01%. Neutral equivalent'2793.

Found: C,- 64.83%; H, 7.72%; N, 5.06%. "Neutral equivalent 281.3.

Preparation of the N-carboanhydride of alphaamino-alpha,gamma-diethg loaleric acid In a reactor open to the atmosphere only through a drying tube, a mixture of five parts of the above N-carbobenzyloxy-alpha-aminoalpha,gamma-dimethylvaleric acid and 4.3 parts of thionylchloride in 17.7 parts of anhydrous diethyl ether is refluxed for six hours and allowed to'standat room temperature for an additional eleven hours.- The clear colorless solution is evaporated to give aviscous' oil. Trituration with excess petroleum ether at ice-saltbath temperature brings about crystallization, and

cooling the mixture at solid carbon didxidtmperature. The crystalline product is removed ,by filtration under anhydrous conditions.

.There is thus obtained pure N carbonanhydride of alphaamino alphagammae dimethylvaleric acid as crystals melting sharply at 32.7-33.0 C. 1

Analysis.--'Calculated forcaHiNQaz C. 56.12%; H, 7.66%; N, 8.18%. Found: C, 55.35%} H, 7.66%;N,8.12%. I

EXAMPLE XV POLYAMIDE FROM ALPHA-AMINO-ALPHA,GAMMA- alpha-arnino-alpha,gamma-dimethylvaleric acid.

is heated slowly to 222 C. in a; narrow reactor open to the atmosphere at one end. When. the temperature reaches this point, the liquid melt evolves gas bubbles and there is obtained an alpha-amino-alpha,gammadimethylvaleric acid polyamide as a'n opaque; thermally stable sol-id;

Although inthe-ioregoing examples certain conditions of reaction time, temperature, proportion, etc. have been given for the preparation of selected examples of the N-carboanhydrides of this invention, it is to be understood that these conditions may be varied in accordance with the general methods hitherto employed in the preparation of N-carboanhydrides of other amino acids.

The present invention is generic to alphaamino acid N-carboanhydrides of the following type formula wherein R and R are primary alkyl groups and R is CmlH2m-l where m is an integer, the total number of carbons in R, R, and R" is from 3 to 6 and these carbons are alkyl carbons, i. e., carbons of alkyl groups.

Of general utility in the preparation of these N-carboanhydrides are monoamino alkane monocarboxylic acids, 1. e., aminoalkanoic acids of the formula recurring alpha-amino acid units 10 to 100% of which are units of the formula wherein R, R, and R are as before. In the case of copolymers there will be recurring structural units of other alpha-amino acids.

Upon hydrolysis with (concentrated aqueous) hydrochloric acid for hours at 150 C. under autogenous pressure in an autoclave, all the polymers of this invention yield at least one amino acid of the general formula wherein R, R, and R" are as before. The alphaamino acids will be found as the hydrogen chloride addition salts of which at least 10% by weight are of the formula Rt! HC1.RNH(:3-CO0H The polymers usually have a degree of'polymerization of at least 25, i. e., have at least 25 amino 12' acid units and soften above 125 C. When at least 10% of the recurring units of the polymers are composed of the residues oi amino acids of the above indicated type formula, improvements in thermal stability and organic solubility are noted in the polymers. For this reason, copolymers having more than 10% and preferably more than 50% of the units derived from the above described amino acids are preferred.

As specific examples of alpha-amino acids other than those mentioned previously whose N-carboanhydrides can be op lymerized with the N- carboanhydr-ides of: this. invention there may be mentioned for example: valine, alanine, leucine, norlellcine',. isoleucine, methionine, tyrosine, sarcosine. (Ne-methylg-lycinel, N-phenylglycine, 1.- aminc cyclopentanecarboxylic acid, 1-amino-2- methylcyclohexanecarboxyiic acid.

The pclyamides and copolyamides of this in- QntiQn are. prepared optionally in the presence of organic liquids by the condensation polymerization (thermal or initiated by water, alcohols, phenols, organic acids, or amino hydrogen-containing amines) of the previously defined alphaamino acid N-carboanhydrides with carbon dioxide evolution. Suitable organic liquids that can be used include pyridine, aromatic hydrocarbons, such as: benzene, xylene, etc; halogenated hydrocarbons, such as: carbon tetrachloride, chloroform, chlorobenzene, etc.; cyclohexane, glycol diethyl ether, and dibutyl ether. The N-carboanhydrides are suitably heated, in a vessel "adapted to permit escape ofcarbon dioxide, to that temperature at which carbon dioxide begins to be evolved at an appreciable rate under the conditions of reaction. This varies with different amino acids, but it is usually at temperatures from 25 to 200 C. and is generally within 50 C. of the melting point of the N-carboanhydrides and in the case of mixtures within 30 of the lowest melting N-carboanhydride. The time of the reaction can be shortened or the temperature necessary can be lowered or both can be accom- D s y the Q reaction initiators, e. g., water, alcohol, phenols, organic acids or amino ydroeenec nte n ns m n s.-

The polyamides and copolyamides of this invention can be used to produce films and fibers. They a c e s d n. m ld n d. coa n compositions. These polyamides. are soluble in one or more of the following: water; sulfuric acid; five and six' membered alicyclic ketonesv iqu d below f r am l oyc opentanon d yq ohox one; halogenated hrci l oa b ns liqu ow -i a me hy e ride. hloi a on tetr c o i e. cm obenzen 1.2- di-chloroethane; alcohols, e. g., ethyl alcohol and p pr alcohol; and p n ls and. thiopmi olsv liquid below '15. C. for example, phenol, chlorop onol, mreso t i n en l. and. or i monomethyl therh se. nolyamides a be plas ed ith. hi h. b ling compou ds s h as. polychlorinated diphenyl ether and camphor. The novel polyarnideaof this invention are outand n n hat th y ex ibit. od. th mal stability ounte it sp nbility in a wide range. o organic solventsa combination of properties long desired for fiber and film outlets.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitationsv are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

13 What is claimed is: 1. An N-earboanhydride of the formula wherein R and R are primary alkyl groups, R" is CnH2n+1 where n is a cardinal numeral and the carbons in R, R, and R" are all alkyl carbons and total from three to six.

2. An N-carboanhydride of the formula RC-0 0 o H-N-O 0 wherein R and R are primary alkyl groups totaling from three to six carbons.

3. An N-carboanhydride of the formula wherein R and R are primary alkyl groups, R is an alkyl group and R, R, and R" total from three to six carbons.

4. An N-carboanhydride of the formula wherein R, R, and R" are primary alkyl groups and total from three to six carbons.

5. A filmand fiber-forming polymer whose recurring units are alpha-amino acid units, 100% of which are of the formula wherein R and R are primary alkyl groups, R is CnH2n+l where n is a cardinal numeral and the carbons in R, R, and R" are all alkyl carbons and total from three to six, which polymer has a degree of polymerization of at least 25.

6. A filmand fiber-forming polymer whose recurring units are alpha-amino acid units, 10-

100% of which are of the formula RI! R! -z I-c-o 0 wherein R, R, and R" are primary alkyl groups and total from three to six carbons, said polymer having a degree of polymerization of at least 25.

7. A polymer according to claim 6 wherein 10- 100% of the recurring units are of the formula 8. A 111mand fiber-forming polymer which on hydrolysis with aqueous HCl for hours at 150 C. under autogeneous pressure in an autoclave yields a composition consisting essentially 14 of alpha-amino acid hydrochlorides of which 10 to is of the composition wherein R and R are primary alkyl groups, R" is of the formula CnH2n+1 wherein n is a cardinal numeral and the total carbons in R, R, and R" are alkyl carbons and number from three to six. 9. A filmand fiber-forming polymer which on hydrolysis with aqueous HCl yields a composition consisting essentially of alpha-amino acid hydrochlorides of which 10 to 100% is of the composition wherein R and R are primary alkyl groups, n is a cardinal numeral and the total number of carbons in the amino acid hydrochloride is from five to eight.

10. A filmand fiber-forming polymer whose recurring units are alpha-amino acid units, 10- 100% of which are of the formula wherein R and R are primary alkyl groups totaling from 3 to 6 carbons.

11. A polymer according to claim 10 wherein l01100% of the recurring units are of the formu a 62H} -NH-co0- 12. A polymer according to claim l0 wherein 10-100% of the recurring units are of the formula 133A polymer accordingto claim 10 wherein 10-1100% of the recurring units are of the formu a Number Name Date 2,293,388 Hanford Aug. 18, 1942 2,327,162 Baldwin et al Aug. 17, 1943 2,516,145 Prichard July 25, 1950 2,517,610 Tullock Aug. 8, 1950 FOREIGN PATENTS Number Country Date 555,129 Great Britain Aug. 5, 1943 OTHER REFERENCES Oiiice of Technical Services, PB 34279, 3 pages, December 13, 1946. 

6. A FILM- AND FIBER-FORMING POLYMER WHOSE RECURRING UNITS ARE ALPH-AMINO ACID UNITS, 10100% OF WHICH ARE OF THE FORMULA 